The invention relates to determining a depth.
Determining a depth or a distance, also known as range sensing, is important in, e.g., industrial applications such as measurement of solder paste volume in manufacturing surface-mounted electronic assemblies, digitization of three-dimensional ("3-D") clay models, and inspection of semiconductor packages for lead coplanarity.
Electronic devices that have traditional electrical terminals (e.g., dual in-line package leads) may be inspected in two dimensions using backlight. However, some devices that have other types of electrical terminals such as ball grid array balls cannot be effectively inspected using backlight. Instead these devices are inspected by an imaging system that can view the terminals in three dimensions to check for compliance with specifications for, e.g., height, volume, and shape.
Optical systems have been devised that allow 3-D images to be derived from two-dimensional ("2-D") images, by exploiting optical principles that relate the extent to which a surface is out-of-focus to a distance between the surface and an in-focus point. With such systems, resulting depth information in each of the derived 3-D images has only a fraction of the resolution of each of the 2-D images (e.g., only 512.times.512 points of depth information from 1024.times.1024 2-D images). Thus, to derive depth information having only moderate resolution, such systems are compelled to use costly high-resolution cameras that can produce the necessary high-resolution 2-D images.